Radiant steam generator



July 22, 1947. L L, L MARSHALL r2,424,476

RADIANT STEAM GENERATOR Fiied neme?, 1943 275 Je 51d/ MHHIIHH /27 m f .Hun/VER l '6.

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L INVENToR. [award .[/fafJa/Z L Byn Q Patented July 22, 1947 RADTANT STEAM GENERATOR Leonard J. Marshall, Tenaily, N. J., assignor to Combustion Engineering Company, Inc., New

York, N. Y.

Application December 27, 1943, `Serial No. 515,713

2 Claims. 1

This invention relates to steam generators and particularly to those equipped with superheaters.

The trend in steam generating units toward higher steam pressures and temperatures and high capacities has introduced new experiences into operation that indicate the necessity of essential changes in the apparatus and in the operation of the units. With the trend toward higher superheated steam temperatures, the combustion rates within the furnaces were increased in order to obtain hotter gases passing over the convection superheaters, and these were placed closer to the furnace. The higher combustion rates and higher furnace exit temperatures in turn produced more slag deposits on the superheater tubes thereby requiring greater cleaning efforts in order to keep the gas lanes between the tubes open and also added to the difculties of controlling superheat temperatures. The higher combustion rates within the furnace and the higher steam pressures combined to reduce the allowable margin in temperature rise for the furnace water wall tubes before deterioration by overheating would occur. The higher combustion rates increased the rates of radiant heat input to the furnace wall tubes and the higher steam pressures contributed in increasing the tube temperatures because of the higher evaporating temperatures of the water and by the slower water circulation through the tube circuits due to greater densities of the steam and lesser densities of the water. Y

Although the furnaces become smaller with the increased combustion rates, the higher-temperature of the gases leaving the furnace require an increased amount of boiler convection surface for absorbing the added heat. Correlated with the convection-surface and the superheater surface are by-passes for conveying a portion of the gases around the superheater with by-pass dampers for controlling the gas flow, thereby regulating the temperature of the superheated steam. These by-passes are of substantial size to accommodate the quantity of by-passed gases required for adequate superheat control and it has been found that in some cases the range of control is not sufficient to meet the requirements of the users. As was to be anticipated, the draft loss through enlarged convection surfaces ofthe unit rose, causing an increase in the power required for overcoming this loss.

It is an object of this invention to provide. an improved steam generating unit that will overcome the above described difficulties.

In the drawings Figures l and 2 are diagrammatic sectional elevations of steam generating units embodying the invention.

Figure 3 is an enlarged sectional elevation through the furnace Wall to show the mounting of the burners.

The invention contemplates a radiation boiler in which the furnace is of such size in relation to the combustion rates and to the amount of heat absorbing tube surface in the form of steam generating tubes on the furnace walls that the heat absorption by said tubes suiiices to evaporate all of the steam to be produced by the generator and yet not result in an excessive rate of heat absorption in any 0f such surface that would result in overheating the tubes. Further, the combustion within the furnace is principally confined to a hot zone which is controlled as to its location and extent, the zone being shifted upwardly and downwardly within the furnace in a manner that Varies the amount of heat absorption by the whole boiler surface and therewith varies the temperature of the gases leaving the furnace. This temperature control of gases leaving the furnace has the dual purpose of maintaining the gases at a slag-free temperature when entering the superheater convection surface and of controlling the superheat temperature by varying the gas temperature. Due to the combination of the control of the location of the hot` zone of combustion and to the rela- I tively low combustion rates, the invention further contemplates supplementing the convection superheater by the use of radiant superheater tubing on the furnace walls located safely beyond injurious effects of the hot zone, thereby limiting the rate of heat radiation to any of the superheater tube surface and avoiding overheatlng said surface.

Furnace I0 of rectangular cross section is provided with fuel burners I2 preferably located at the corners within the bottom half of the furnace. On the front wall I3 of the furnace the lower portion adjacent the burners is provided with steam generating tubes I4 extending downwardly from a header Illa to the ash pit I5 and forming a portion of the sloping bottom. In Fig. 1 the upper portion of the front Wall is provided with superheater tubes I6 located intermediate the upper parts Mb of the wall tubes and which extend from a header II downwardly through offtake I8 thence under the furnace roof I9 to front wall I3 and downwardly to enter a header ZI.

The rear furnace wall 22 is faced with steam generating tubes 23 extending downwardly from steam and water drum 24 for the entire length of the wall from drum 24 through the oiftake I8 to the ash pit I5. On the upper half of rear wal1 22 the tubes 23 are bent to form a ledge-like baille 25 projecting into the furnace for shielding the offtake I8 and convection superheaters 2B and 29 from the radiant heat of the furnace. Baiile 25 lies wholly within the limits of furnace I0. The slide walls 2'!l are provided with steam generatingy tubes that extend from ashv pit I5 to the furnace roof I9 and into a header 2lb, and a portion of them continue upwardly on the sidewalls of the offtake I8 into a header 21e.

Located in the top of the furnace and above baille is a superheater section 2.6 which isy connected to outlet header 3| for therradiant surperheater and to steam outlet header 28. Located in the offtake I8 is another convection su. perheater section 29 which is ahead of radiant superheater I6 in the direction of steam flow; its tubes being connected to inlet header 30 and intermediate header II, which isl the inlet header for radiant superheater I6 the former header being connected to the steam and. water drum 24. Note that the convection superheate-r sectionl 29 is enclosed by extensions 23A, 21A of the* water wall surfaces ofthe rear and side furnace walls and by superheater tubes IG from the front wall I3. This construction does away with` structures such as heretoforel usedI employing heavy brick or sectionally supported walls at the sides of the superheater bank, which constructions were -objectionable because they werecostly, were subject to cracking and` consequent leakage and requiredsubstantial insulation to prevent heat loss from the high temperatures within.

In some instances it may be desirable tol provide a radiant superheater havingv three sections,v

as shown in Fig. 1, in place of one, the first sec-V tion I6 being located onk front Wall I3 and the other tWo sections respectively on the two side walls. through convection superheater section 29- to` intermediate-header I'I, thence through super-heater section I6 down thef-ront wall of offtake I8, along,

roof I9 and down the front wall I3 to a header 2l. From header 2| the steam passes to the two side wall headers 3-2 at the bottom of the two sidewall superheater sections IGS. From headers 32 steamflows upwardly' through theV side wall sections IGS to headers 33 that discharge into a common header SI. steam` flows through convection superheater section 2.6. and up to outlet header 28.

The above described arrangement of radiant and convection superheaters in combination produce a superheat temperature that does not vary much from the normal.

The burners are of the type shown in a copending application of Kreisinger et al., Serial No. 420,356,` led November 25, 1941, and issuedI as U. S. Patent No; 2,363,875, dated November 28', 194'4. At each corner of the furnace there are several superimposed burner nozzles 34:, one of which is shown in Fig. 3; eachburner is ca pable of vertical adjustment to direct the fuel stream issuing therefrom upwardly or downwardly into the furnace; a further horizontali adjustment enables the fuel streams to bedirected at various angles in a horizontal plane so that in general the ruel. streams are projected tan gentially to an imaginary-verticalzcylindricalsurface located preferably at the center of the furnace. This tangential directionA of the fuel streams causes a turbulent combustion within a limited zone about the location wherethey m- Steam flows from drum 24 to header 30 From= header 3| the.

4 pinge upon one another. When the fuel streams are pointed downwardly toward the lower portion of the furnace, the zone C of intense combustion is moved toward the bottom of the furnace and causes the maximum amount of heat to be absorbed by radiation by the bottom parts of steam generating tubes adjoining the zone. When the f-uelA streamsare directedl horizontally, the zone off combustion A is adjacent the burners and the maximum rate of heat absorption is by the tube portions adjacent the burners. When the fuel streams are directed upwardly the zone of' combustion B at the upper part of the furnace will moveto a location above the burners and the highest rate of heat absorption is by the tube portions above the burners. It will be seen that as, the zone of combustion is shifted upwardly the lower parts of the furnace walls receive less heat and the upper portions receive more with the result that the temperature of gasesleavng the furnace is higher, As the zone of combustion is shifted further upwardly the radiant portion I6.. 16S of the superheater surface is exposed not only to hotter gases but a-lsoy to amore directradiation from the zone of combustion andl the convection. sections of the su.- perheater receive hotter gases. In this manner a wide range in. control of superheat may be obtainedl A further advantage, is, that as the hotv zoner of combustion is moved downwardly with in.- creased loads to. increase the'amount of heat ab.- sorbed, byV the, furnace water walls to make more steam, the. relative amount of heat absorbed by thev radiant superheater tubes also decreases to control the superheat. In this manner the radiant superheater isprotected from overheating at the higher ratings.

A` relatively small by-pass 4D` and damper 4I may be provided around superheater 29. which will permit a, further refinement in superheat control.

Becauseof the relatively large furnace in which combustion rates have been deliberately keptlow, the. radiant. heat absorption of the steam generating tubes, even at the hottest zone of com.- bustion isz kept relatively low and therefore does not tend to. overheat the tubes. Because of the relatively largefurnace the steam generating surfacefwi-thin the' furnace has been made large soV that it sunices to evaporate al1 of the steam tobe produced by the generator andl no further convection surfaceV for steam generation is necessary. Because` off the relatively large furnaceand the amount. ofboiler surf-ace,y the temperatures of gases leavingA the furnace. are relatively low and' the usual screen for shielding the convection superheater becomesl unnecessary. The omission of sucha screen has the advantage of eliminatingythev obstruction that it offers tothe slag particles-.flowing down the baffle 25` to drop thence into the furnace. Thelow temperatures of gases leaving thefurnace permit the use of a close spac-I ing: of the convection superheater tubesv since the former 'slaggingp diiculties havebeen minimized.

Because the combination of a radiant super-- heater and' convection super-heater produces a relatively uniform superheatl temperature over a considerable load variation, this characteristicA combined with the ability' of further controlling the superheat temperature by burner manipula.- tion;J asis: the; case in the improved generator, resultsin a wider rangeofv superheat control.,

In Fig. 2 the upper portion of the front Wall is provided with superheater tubes I6 which extend from header I 'I downwardly thrgh furiia oilitake I8 thence under the furnace roof I9, in spaced relation, to front Wall I3 and downwardly along its face to return bends 20. From bends 20, these tubes run upwardly intermediate the downwardly directed parts along the front wall I3 and roof I9 but before reaching the furnace offtake I8 rise through the roof I9 to enter header 3Ia. Risers I4c from header I4a and wall tubes I4, pass upwardly within the Wall I3 and roof I9 where they lie adjacent the superheater tubes I6. After leaving roof I9 risers I4c pass up through offtake I8 along its front wall and into the steam and water drum 24. Although the side wall tubes adjacent the superheaters are not shown in full, they continue upwardly to form the inner face of the furnace offtake I8. Their partial omission in the drawing is to avoid conflict with the showing of the superheaters.

What I claim is:

1. In a steam boiler, means forming a vertical furnace chamber having a substantially horizontal gas outlet passage leading to a vertical boiler oitake Within the horizontal limits of the chamber at the upper part thereof; steam generating means consisting of heat absorbing water circulating tubes mounted on all of the furnace walls extending continuously from the bottom tothe roof of the furnace certain ones of which continue beyond the furnace to face some of the walls of the outlet passage; means for burning fuel in said furnace; a convection superheater for heating the steam leaving the boiler disposed wholly within said outlet and thereby shielded from direct exposure to the radiant heat of the burning fuel in said furnace; the amount of steam generation surface comprising wall tubes in the furnace and outlet passage being sufficient to evaporate all of the steam required from the boiler.

2. In a steam boiler; means forming a vertical furnace chamber having a substantially horizontal gas outlet passage leading to a vertical boiler' offtake within the horizontal limits of the chamber at the upper part thereof; steam generating means consisting of heat absorbing water circulating tubes mounted on all of the furnace walls extending continuously from the bottom to the roof of the furnace certain ones of which continue beyond the furnace to face some of the walls of the outlet passage; means for burning fuel in said furnace; a convection superheaterl for heating the steam leaving the boiler disposed wholly within said outlet and thereby shielded from direct exposure to the radiant heat of the burning fuel in Said furnace; the amount of steam generation surface comprising wall tubes in the furnace and outlet passage being sufficient to evaporate all of the steam required from the boiler, while the related heat released by the fuel within the furnace is below that at which the temperature of the gases entering the outlet will cause slagging of the ash to occur on the superheater tubes without the interposition of any water cooled screen.

LEONARD J. MARSHALL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,223,199 Armacost Nov. 26, 1940 2,212,115 Ebbets et al Aug. 20, 1940 2,100,190 Jackson Nov. 23, 1937 2,109,840 Gordon Mar. 1, 1938 2,368,629 Beach Feb. 6, 1945 2,126,260 Jackson Aug. 9, 1938 2,213,185 Armacost Sept. 3, 1940 2,250,849 Wood July 29, 1941 1,935,635 Jacobus Nov. 21, 1933 2,363,875 Kreisinger et al. Nov. 28, 1944 1,887,854 Lasker Nov. 15, 1932 

